After I clean an engine, I use Lemon Pledge furniture polish to shine up my old postwar trains. Works great, and doesn’t leave a greasy residue, and I use cotton swabs in all the nooks and crannys. Takes time, but its worth the effort, and makes them look almost like new. You are one lucky dude, that engine is rare.[;)]
I’ve been using Pledge on my die cast locos and plastic diesel shells since about 1960. No greasy residue, brings the gloss up, and best of all…the paints has held up.
Washing was with a very mild dish soap/lukewarm water solution. Midew is his problem, though.
Jack